Sound dampening pads are used in the doors of cars and other automotive vehicles to absorb, deflect, or otherwise mitigate transmission of sound from outside of the vehicle to the cabin. Such pads can be deployed between door panels, within the interior of the door itself, where space constraints limit the size and shape of the pad. Limits to the size and shape of sound dampening pads can correlate to limitations of the pads' ability to decrease sound transmission to the vehicle cabin.
The amount of space theoretically available to house a sound dampening pad in some contexts may not be consistent over time. For example, within the context of an automotive vehicle door having a reversibly openable window, the amount of space available to house a sound dampening system can be greater when the window is up as opposed to when the window is down. A sound dampening system which has a fixed, non-varying shape and size is incapable of utilizing this extra space.
Beyond the composition and structure of individual sound dampening pads, the use of two sound dampening pads arranged in parallel, i.e. a double-wall system, can have significant effects on sound dampening capability. In some circumstances, a double wall system having a larger distance of separation between the two walls or pads will have significantly greater sound dampening capability as compared to a double wall system with a smaller or no distance of separation between the two walls or pads. Additionally, differences in the separation space between two pads or walls of a double wall system can alter the frequency response of the system.